Jane, You have gotten some excellent responses from the great people and players on this board.
I agree with Dusty, that while wood can definitely affect the timbre of your instrument, it has much more to do with how the instrument is built, and how it is played.
I find that paying great attention to my technique, using as little pressure as possible when I fret, and using a light touch on my picking hand. Regardless of whether I'm finger picking or using a pick to strum I have to be careful of how I'm playing... not digging into the strings very hard to play them, but getting a nice brush on top of the strings to set them vibrating.
I have personally found that the longest VSL my body can manage seems to also help me as far as sustain goes... so while you don't want an instrument that is too long for your body, you don't want to go too short either.
Size, build, materials and technique all play their own part in the tonal quality of your sound.